Silicate two-component coating composition

Abstract

The present invention relates to a silicate two-component coating composition, comprising a) a first aqueous component, containing 2 to 25 wt.% of at least one mineral, alkali-stable pigment, 20 to 75 wt.% of at least one filler, and 0.5 to 5 wt.% of at least one hydrophobing agent, selected from hydrophobing agents based on polysiloxanes, silanols and / or stearates, wherein the wt.% relate to the total weight of the first aqueous component, and b) water glass, selected from soda water glass, potash water glass and / or lithium water glass, with a molar ratio of at least 2.6 as the second component, wherein the silicate two-component composition is free of polymers and VOCs. The present invention also relates to a method for applying a two-component coating composition onto a substrate, a coated substrate obtainable by said method, and the use of the silicate two-component coating composition according to the invention for coating a mineral substrate.

Description

[0001] SILICATE TWO-COMPONENT COATING COMPOSITION

[0002] The present invention relates to a silicate two-component coating composition comprising a) a first aqueous component containing 2 to 25% by weight of at least one mineral, alkali-stable pigment, 20 to 75% by weight of at least one filler, and 0.5 to 5% by weight of at least one hydrophobizing agent selected from hydrophobizing agents based on polysiloxanes, silanols and / or stearates, wherein the % by weight is based on the total weight of the first aqueous component, and b) waterglass selected from soda waterglass, potassium waterglass and / or lithium waterglass, with a molar ratio of at least 2.6 as the second component, wherein the silicate two-component coating composition is free of polymers and VOCs.The present invention further relates to a process for applying a two-component coating composition to a substrate, to a coated substrate obtainable by this process, and to the use of the silicate two-component coating composition according to the invention for coating a mineral substrate.

[0003] The topic of sustainability has now also become highly relevant for the field of construction chemicals. In Germany alone, over 500 million tons of mineral raw materials such as lime, gypsum, gravel, and sand are used every year, contributing to environmental pollution. The construction industry therefore consumes a lot of resources, but building materials are still difficult to recycle and reprocess. This is due, among other things, to the large quantities of plastic composite materials used in construction chemicals. For example, polymers are used as binders and sometimes as additives in paints and varnishes, making them essential components of coatings. Furthermore, paints and varnishes are also responsible for a large proportion of microplastics in the environment. Since the main components of architectural paints are generally polymer-containing binders, the polymer particles contribute to the release of microplastics through abrasion and weathering.It is assumed that paints and varnishes as a source of microplastics outweigh all other sources of microplastics (e.g. textile fibers and tire abrasion).

[0004] Against this backdrop, there is a need for sustainable alternatives, particularly for coating compositions that avoid the use of polymers, thus improving the possibility of recycling building materials and simultaneously preventing the release of microplastics. A suitable alternative is generally water glass-based binders, which have proven themselves outstandingly effective in the facade and construction industries for centuries due to their good mechanical properties, high water vapor permeability, low susceptibility to dirt, and, last but not least, their ecological potential. Two-component ("2K") silicate paints such as Histolith® Kristallin from Caparol are well-known on the market. Such paints are intended particularly for the renovation of historic buildings to create a lime-like and durable coating on lime and lime-cement plasters.However, the properties of such conventional silicate paints are still insufficient for application on a wide variety of mineral substrates, such as fresh concrete substrates or fresh fiber cement substrates, i.e. substrates that are not older than 8 hours.

[0005] The present invention is therefore based on the object of providing a silicate coating composition for a wide variety of mineral substrates, such as concrete substrates or fiber cement substrates, which (i) is free of polymers and other organic components (VOCs, "volatile organic compounds"), (ii) exhibits low dirt adhesion, (iii) low water vapor diffusion resistance, and (iv) is recyclable. In addition, the coating according to the invention should be resistant to the effects of humidity and temperature changes over a period of several years, thus preventing mechanical damage such as efflorescence and frost damage to the mineral substrate.

[0006] This object is achieved by the embodiments characterized in the claims. According to the invention, a silicate two-component coating composition is provided, comprising a) a first aqueous component containing 2 to 25% by weight of at least one mineral, alkali-stable pigment, 20 to 75% by weight of at least one filler, and 0.5 to 5% by weight of at least one hydrophobizing agent selected from hydrophobizing agents based on polysiloxanes, silanols, and / or stearates, the weight percent being based on the total weight of the first aqueous component, and b) waterglass selected from soda waterglass, potassium waterglass, and / or lithium waterglass, with a molar ratio of at least 2.6 as the second component, wherein the silicate two-component coating composition is free of polymers and VOCs.

[0007] The coating composition according to the invention is a two-component coating composition, hereinafter also referred to as a "2K coating composition" or "2K composition." This refers to a coating composition whose at least two components are usually transported and stored separately and which are mixed together in a specified ratio as shortly as possible before processing (i.e., before application to a substrate).

[0008] The 2K composition according to the invention comprises a first aqueous component. This first aqueous component contains at least one mineral, alkali-stable pigment. Due to the strong basicity of the silicate binder, the pigments used should be alkali-stable. Desired properties such as good hiding power, storage stability and weather resistance of the silicate paint can be achieved through suitable pigmentation. Any suitable mineral, alkali-stable pigment can be used. This is preferably selected from the group consisting of titanium dioxide, iron oxide red, iron oxide black, iron oxide yellow, cobalt blue, chromium oxide pigments, spinel phase pigments and combinations thereof. More preferably the pigment is iron oxide red. The first aqueous component contains 2 to 25 wt. %, preferably 5 to 20 wt. % and particularly preferably 10 to 15 wt. % of pigment. The wt.-% of the total weight of the first aqueous component.

[0009] This first aqueous component further contains at least one filler. According to DIN 55 943, a filler is defined as a “substance consisting of particles, practically insoluble in the application medium, which is used to increase the volume, to achieve or improve technical properties and / or to influence optical properties.” Any suitable filler can be used within the scope of the present invention. The filler is preferably selected from quartz powder, precipitated or fumed silica, barium sulfate, magnesium carbonate, dolomite, calcium carbonate and combinations thereof. The filler is particularly preferably magnesium carbonate, calcium carbonate, a mixture of magnesium carbonate and calcium carbonate or a mixture of calcium carbonate and silica. The fillers used can be coarse-grained and / or fine-grained. The first aqueous component contains 20 to 75% by weight, preferably 25 to 65% by weight.-% and particularly preferably 40 to 55 wt.% of filler. The wt.% refers to the total weight of the first aqueous component.

[0010] This first aqueous component further contains at least one hydrophobizing agent selected from hydrophobizing agents based on polysiloxanes, silanols, and / or stearates. Calcium stearate is preferably used as the hydrophobizing agent. The first aqueous component contains 0.5 to 5 wt.%, preferably 1 to 4 wt.%, particularly preferably 2 to 3 wt.% of hydrophobizing agent. The wt.% are based on the total weight of the first aqueous component.

[0011] In addition, the first aqueous component may also contain further additives. Preferably, the first aqueous component contains one or more additives selected from thickeners (e.g., hydroxyethylcellulose), defoamers (e.g., modified fatty acids, silica, oxyalkylated compounds, emulsifiers), dispersants, wetting agents (e.g., organomodified polysiloxane), and stabilizers (e.g., low-viscosity aqueous solutions of specific hydrophilic alkoxylated alkylammonium compounds). The pH of the first aqueous component is not particularly limited. However, it preferably has a basic pH, particularly preferably a pH in the range of 10 to 13.

[0012] The 2K composition according to the invention further comprises waterglass, selected from soda waterglass, potassium waterglass, and / or lithium waterglass, as a second component. For the purposes of the present invention, waterglass is understood to mean an aqueous solution of an amorphous alkali metal silicate. The waterglass typically contains in the range of 10 to 40 wt. %, preferably in the range of 25 to 35 wt. %, alkali metal silicates, particularly preferably in the range of 28 to 32 wt. % alkali metal silicate. This is the solids content of the waterglass. The alkali metal silicate is sodium, potassium, or lithium silicate. The waterglass is preferably potassium waterglass.

[0013] In addition to the water glass, the second component may optionally contain other components, such as suitable additives. However, the second component preferably consists of the water glass.

[0014] The water glass used in the 2K composition according to the invention has a molar ratio of at least 2.6. This molar ratio (MOR; occasionally also referred to as "modulus") indicates the ratio of silica (expressed as SiC) to alkali oxide (expressed as Me2O: Na2O, K2O, Li2O) and is defined as follows in the context of the present invention. where MVG is the molar ratio, n(SiO2) is the molar amount of silica and n(Me2O) is the molar amount of alkali oxide.

[0015] A potassium water glass with a solids content of 30 wt.%, which contains, for example, 232 g / l silicate species, expressed as SiO2, and 143 g / l potassium oxide, expressed as K2O, has, taking into account the molar mass of SiO2 (60 g / mol) and K2O (94.2 g / mol), an MVZ of (232 g / l 160 g / mol) / (143 g / l 194.2 g / mol) = 2.55.

[0016] Depending on the molar ratio, water glasses are generally divided into the following groups:

[0017] • Alkaline or low-modulus water glasses: MVZ < 2.5

[0018] • Neutral or medium modulus water glasses: MVZ = 2.5 - 3.4

[0019] • High silicic acid or high modulus water glasses: MVZ = 3.9 - 4.3

[0020] A typical property of water glasses is that with increasing modulus, the curing rate increases and the water sensitivity of the formed gels decreases. With increasing molar ratio, the degree of condensation of the silicate species increases. Furthermore, the degree of condensation is directly related to the solids content of the water glasses. The lower the solids content, the higher the water content in the sol, which leads to an increased probability of hydrolysis. Neutral or medium-modulus water glasses, as well as high-silicic acid or high-modulus water glasses, are best suited for the intended applications. According to the present invention, water glasses with an MVZ in the range of 2.6 to 3.4 are preferably used, even more preferably in the range of 2.6 to 3.0. Most preferably, the water glass used has an MVZ in the range of 2.6 to 3.4 and a solids content in the range of 28 to 32%.

[0021] Water glass is generally non-film-forming, and the resulting coatings are extremely porous. Due to their porosity, water glass coatings exhibit excellent water vapor and carbon dioxide permeability. This allows the silicate binder to penetrate the mineral substrate and ensure moisture exchange between the masonry and the surrounding air. Furthermore, due to their chemical similarity to mineral substrates, water glass coatings have similar thermal expansion coefficients. Therefore, even with large temperature fluctuations, tension will not develop between the substrate and the coating. However, their porous nature promotes capillary water absorption, which can lead to moisture-related damage over time.Accordingly, the invention provides for the use of hydrophobic agents in water glass coatings in order to reduce capillary water absorption.

[0022] Furthermore, the silicate coatings according to the invention have an antistatic effect, preventing dust and dirt particles from accumulating on newly applied coatings, thus reducing their susceptibility to dirt. Furthermore, silicate coatings exhibit good weather and chemical resistance. Due to their high alkalinity, the alkali water glasses used can also replace the algicidal and fungicidal effects of standard biocides. This property is therefore advantageous in terms of environmental relevance. According to the invention, the exclusive use of inorganic pigments ensures effective and long-term color stability, which is additionally supported by potassium water glass.

[0023] The composition according to the invention is a two-component coating composition, i.e. the first and second components are initially separate from one another (i.e. are transported and stored separately) and are usually only mixed immediately before use. The first component and the second component are preferably present in a weight ratio of 1:0.8 to 1:5, i.e. they must then be mixed in this ratio before use. This does not, of course, mean that the containers in which they are transported and stored separately must also have these weight ratios. The first component and the second component are preferably used in a weight ratio of 1:0.9 to 1:3 and particularly preferably in a weight ratio of 1:1 to 1:2.

[0024] Finally, the silicate two-component coating compositions according to the invention are free of organic compounds, in particular free of polymers and VOCs (“volatile organic compounds”). In the context of the present invention, a volatile organic compound (VOC) is defined as “an organic compound and the creosote component which has a vapor pressure of 0.01 kPa or more at 293.15 K or has a corresponding volatility under the respective conditions of use.” 1understood (cf. the EU Industrial Emissions Directive 2010 / 75 / EU, Art. 3(45)). According to a preferred embodiment of the present invention, the polymers are selected from the group consisting of polymer microplastics (SPM; “Synthetic Polymer Microplastics”). In this case, in addition to VOCs, only polymer microplastics are excluded from the compositions according to the invention. Microplastics or polymer microplastics are referred to as solid, water-insoluble synthetic polymer particles with a TG>20°C, which may optionally contain additives or other substances, and in which more than 1% (w / w) of the particles have all dimensions less than 5 mm or a length of less than 15 mm and a length-to-diameter ratio of more than 3. Consequently, in this preferred embodiment, no soluble polymers (i.e.Polymer with a solubility of less than 2 g / L), larger polymer particles, or polymers formed by polymerization in nature are excluded. Within the scope of the present invention, the term "free from" is further understood to mean that the 2-component composition may contain a maximum of 0.5 wt.%, preferably a maximum of 0.1 wt.%, of the excluded compounds.

[0025] The 2K compositions according to the invention thus do not require a polymer dispersion component, i.e., they do not require a polymer-containing binder or polymer particles, which contribute to the removal of microplastics through abrasion and / or weathering. The compositions according to the invention have the further advantage that they do not require the addition of a biocide. They are therefore advantageous from an environmental perspective. Furthermore, the 2K compositions according to the invention are advantageous over corresponding 1K compositions in that the reaction rate can be better adapted to the production processes, thus enabling more flexible process control, and that they lead to more robust coatings (i.e., coatings with greater abrasion resistance). The present invention further relates to a method for applying a two-component coating composition to a substrate, which comprises the following steps:

[0026] (a) providing a two-component coating composition according to the invention and a substrate to be coated,

[0027] (b) mixing the first component and the second component in a ratio ranging from 1:0.8 to 1:5 to obtain a mixed coating composition, and then within 1 hour

[0028] (c) coating the substrate to be coated with the mixed coating composition, and

[0029] (d) drying the coated substrate from step (d) for a period in the range of 0.5 to 24 hours at a temperature in the range of 30°C to 160°C.

[0030] In step (a) of the process according to the invention, a two-component composition as described above and a substrate to be coated are provided. The substrate to be coated can be any suitable substrate. The substrate is preferably a mineral substrate, particularly preferably a fiber cement substrate or a concrete substrate. The substrate can be selected in particular from the group consisting of fiber cement panels, concrete roof tiles, and paving stones.

[0031] Fiber cement is a composite material consisting primarily of binder (approx. 40%), additives, reinforcing fibers, process fibers, and water. It also contains air in the form of microscopically small pores. The micropore system allows for the production of a frost-resistant, moisture-regulating, and waterproof building material. Concrete roof tiles, in contrast, are composed of a mixture of cement, quartz sand, water, and color pigments (usually based on iron oxide). Using a special manufacturing process (extrusion), various stone profiles are formed from the resulting "concrete dough." The solidification of the so-called "preforms" takes place in a drying or curing chamber, usually at approximately 50°C for at least 8 hours, followed by further curing in air.Industrially produced concrete roof tiles differ from machine-made concrete roof tiles only in the storage period after the manufacturing process. Machine-made concrete roof tiles are coated with the desired coating immediately after completion. Industrially produced roof tiles, on the other hand, have sufficient time to harden after finishing, as they are typically stored at room temperature for a period of between one day and six months. Over time, this allows the concrete roof tiles to achieve maximum strength without being affected by moisture. Therefore, these concrete roof tiles are often only coated after this storage period.In the context of the present invention, industrially produced concrete roof tiles are understood to mean roof tiles that are only coated after they have completely hardened, while machine-made concrete roof tiles are understood to mean roof tiles that are coated directly after the online-controlled production process (completion) or extrusion.

[0032] In step (b) of the process according to the invention, the first component and the second component of the silicate two-component coating composition according to the invention are mixed in a ratio ranging from 1:0.8 to 1:5. The mixing ratio between the first and second components is preferably about 1:0.9 to 1:3, particularly preferably about 1:1 to 1:2. The actual coating composition, hereinafter also referred to as the “mixed coating composition,” is obtained by mixing the two components. This mixing can be carried out by any suitable method known to the person skilled in the art. The next step then takes place within 1 hour. The first component and the second component are thus mixed essentially immediately before further processing, i.e., before coating, and the mixed coating composition is applied directly to the substrate.Preferably, the time before further processing or coating should not exceed 10 minutes.

[0033] In step (c), the substrate to be coated is coated with the mixed coating composition. This coating can be carried out using any suitable method known to those skilled in the art. Coating can be carried out, for example, in the form of wet coating and / or dry coating. Wet coating refers to the application of the coating composition before the substrate (e.g., the concrete roof tile blank) has cured, immediately after its production. In dry coating, the coating composition is applied to the already cured substrate.

[0034] According to a preferred embodiment of the method according to the invention, the coating is carried out in the form of a dry coating. Most mineral substrates to be coated are already cured materials, so dry coating is the usual method of coating. Preferably, the substrate is stored under dry conditions for a period of at least one day before the coating step (c). More preferably, the substrate is stored for a period of at least 28 days before the coating step (c). This is particularly preferred if the substrate is a fiber cement substrate or a concrete substrate, since such substrates are usually stored before delivery.

[0035] According to another preferred embodiment of the method according to the invention, the coating is carried out in the form of a wet coating.

[0036] According to a further preferred embodiment, after step (b) and before step (c) of coating, which preferably takes place in the form of a dry coating, a further wet coating step (c') takes place. As explained with regard to step (b), this further wet coating step (c') takes place within 1 hour, preferably within 10 minutes, after mixing the first component and the second component. In this additional coating, the mixed coating composition is first applied to the substrate directly after its production and before its curing and then dried for a period in the range of 4 to 48 hours at a temperature in the range of 30°C to 160°C. Only after the wet coating step does the additional coating according to step (c) take place.

[0037] In step (d) of the process according to the invention, the coated substrate from step (c) is dried for a period in the range of 0.5 to 24 hours at a temperature in the range of 30°C to 160°C. Preferably, the drying takes place for a period in the range of 0.5 to 8 hours. If the coating is carried out in the form of a dry coating, a drying period of 0.5 to 1 hour is particularly preferred. If the coating is carried out in the form of a wet coating, a drying period in the range of 6 to 8 hours is particularly preferred. The drying temperature is preferably in the range of 80°C to 150°C, particularly preferably in the range of 100°C to 130°C.

[0038] For improved coating performance, the substrate can be primed before being coated in step (c). However, according to the present invention, it is preferred that the substrate not be primed before being coated in step (c). The coating composition according to the invention is also readily suitable for coating unprimed substrates.

[0039] The present invention further relates to a coated substrate which is obtainable by the process according to the invention described above.

[0040] Furthermore, the present invention relates to the use of the silicate two-component coating composition according to the invention for coating a mineral substrate, preferably a concrete substrate or a fiber cement substrate, particularly preferably for the industrial coating of concrete-containing carrier materials.

[0041] The present invention is described in more detail below using examples.

[0042] Examples:

[0043] The properties of silicate 2K coating compositions were investigated for different substrates depending on the water glass binder used.

[0044] For this purpose, three different commercially available potassium water glasses belonging to the medium modulus class (MVZ between 2.5 and 3.4) were used. The molar ratio, solids content, density, and pH values ​​of the

[0045] Water glasses are taken from the technical data sheets (Table 1 ):

[0046] Table 1 :

[0047] Using the above-mentioned water glasses, the following silicate 2K coating compositions were prepared (Tables 2 and 3):

[0048] Table 2

[0049] Table 3

[0050] To produce the coating, the components were first weighed and pre-dispersed in a dissolver. First, the thickener was placed in a container with deionized water, and both components were stirred in the dissolver for approximately 20 minutes. This step was carried out to ensure the thickener swelled, which subsequently led to pseudoplastic (shear-thinning) behavior of the coating composition. The other components of component A were then added while stirring and thoroughly dispersed at approximately 2800 rpm. Component A was complete after a dispersion time of approximately 20-30 minutes. The binder (component B) was added shortly before (<10 minutes) the coating composition was applied. For this purpose, the required amount of binder was weighed based on a weight ratio of 1:3 (component A: component B) and added to component A.The two components were mixed together for approximately two minutes in a dissolver.

[0051] Industrially produced fiber cement panels and machine-made concrete roof tiles were used as the substrate.

[0052] The coating was carried out in the form of wet coating and / or dry coating either with a film applicator or with a spray gun.

[0053] According to Method 1, a dry coating was applied to a fiber cement board or a concrete roof tile, followed by drying for 24 hours at a humidity of 80% and at a temperature of (a) 50°C, (b) 80°C or (c) 140°C.

[0054] According to method 2, a wet coating was first applied to a concrete roof tile blank immediately after its completion, followed by drying for 8 hours at a relative humidity of 80% and a temperature of 50°C. This was followed by a second coating (dry coating), followed by drying for 1 hour at 50°C. Method 3 is based on method 2, but the final drying step (1 hour at 50°C) was omitted. Here, the concrete roof tile was stored directly after the dry coating without further curing (comparative method).

[0055] Method 4 is also based on method 2, but the wet coating step has been omitted.

[0056] The coated substrates were tested for their efflorescence behavior, frost resistance, and UV resistance. The corresponding measurement methods and results are presented below.

[0057] Efflorescence behavior:

[0058] The samples to be tested were at least 21 days old. Dust was removed using compressed air, brushes, or rags to keep the samples' surfaces clean. For the test, a ring approximately 2 cm in diameter was drawn on the surface of the coated fiber cement board using a commercially available silicone tube. Care was taken to ensure that the drawn ring was closed and fully touched the test surface. After one day, 2 ml of deionized water was poured into the ring and allowed to evaporate at room temperature. This process was repeated three times. After the third application, the sample was dried at room temperature for at least five days so that the hydroxides could convert into carbonates in air. Four weeks after the first assessment, the samples were assessed again (without rinsing), as efflorescence sometimes only appears or becomes more severe after a longer period of time.The resulting efflorescence was visually assessed using the rating scale shown in Table 4.

[0059] Table 4

[0060] For the substrates coated by method 1, the following results regarding efflorescence behavior were obtained for water glasses 1 to 3 (WG 1 to 3) (Table 5):

[0061] Table 5

[0062] It was found that efflorescence decreased with increasing drying temperature. Furthermore, the degree of efflorescence was relatively low for the coating compositions according to the invention with water glasses 2 and 3, even at lower drying temperatures. The coatings according to the invention exhibited generally better resistance to efflorescence. The comparison for the coating composition with water glass 3 showed the following results for efflorescence behavior for the various coating processes (Table 6):

[0063] Table 6

[0064] It was found that a dry coating alone, followed by drying, resulted in the least amount of blooming. However, the combination of wet and dry coating also produced good results, provided subsequent drying was performed.

[0065] Frost resistance

[0066] Test specimens were stored at an angle in a 15 l plastic container (350 x 250 x 180 mm) using spacers and then filled with saline solution (3%) to approximately 2 cm above the test specimens. Depending on the test specimen, they were stored in the saline solution for one day (fiber cement) or three days (concrete roof tiles). The container with the test specimens was then placed in the frost test cabinet. To ensure consistent test conditions, the same number of test containers with a constant load were always placed in the frost test cabinet. The cooling times and temperatures as well as the heating times and temperatures were selected so that the saline solution in the test containers froze completely and then thawed to room temperature. The test specimens were assessed once a week or every ten cycles. One cycle lasted 24 hours.After the warm-up phase, the test containers were removed from the frost test chamber for interim evaluation. The test specimens were rinsed under running water, dried, and assessed. The test specimens were then returned to the containers, which were then placed back into the frost test chamber. The final assessment was carried out after 25 completed cycles. For this purpose, the test specimens were acidified with 5% hydrochloric acid to remove any limescale deposits and then thoroughly rinsed under running water. Visual changes such as blistering or paint flaking were assessed as a percentage (see Table 7). Table 7.

[0067] For the substrates coated by method 1, the following results regarding frost resistance were obtained for water glasses 1 to 3 (WG 1 to 3) (Table 8):

[0068] Table 8

[0069] It was found that water glass 1 (comparison) exhibited significantly greater frost damage. In contrast, the coatings according to the invention with water glass 2 and water glass 3 exhibited better frost resistance.

[0070] UV resistance

[0071] The UV resistance of the coating composition was tested in accordance with DIN EN ISO 16474-2. In this test, coating materials are exposed to laboratory light sources to simulate natural weathering (outdoor weathering). This standard specifies the procedure for exposing sample panels to xenon arc light in the presence of moisture. This allows the effects of weathering to be reproduced. These effects occur when materials are exposed to daylight or daylight filtered through borosilicate glass in their final use in the existing environments. The temperature in the test chamber can be adjusted between 42°C and 120°C, depending on the temperature sensor used (black panel).

[0072] The applied coating systems were evaluated using a time-accelerated test procedure using daylight filters. The planned test duration for waterborne thermoplastic dispersion coatings was 2,500 hours and approximately 4,000 hours for UV-curing thermosets. This test duration consisted of different exposure periods under controlled conditions (e.g., temperature, humidity, and / or humidification) in the order shown in Table 9.

[0073] Table 9

[0074] At the end of the test, the test samples showed a maximum color difference of dE 2 compared to the reference samples; the silicate coating was matt.

[0075] The comparison for the coating composition with water glass 3 showed the following results for UV resistance for the different coating processes.

[0076] Table 10

[0077] As shown in Table 10, the roof tile coated by the process not according to the invention (without final drying) was no longer UV-resistant in the xenon test chamber after only 2 hours.

[0078] In summary, it can be seen that the coating compositions according to the invention exhibit less blooming and improved frost resistance. Furthermore, the process according to the invention is suitable for obtaining such coating compositions.

Claims

Patent claims 1. A two-component silicate coating composition comprising a) a first aqueous component containing 2 to 25 wt.% of at least one mineral, alkali-stable pigment, 20 to 75 wt.% of at least one filler, and 0.5 to 5 wt.% of at least one hydrophobizing agent selected from hydrophobizing agents based on polysiloxanes, silanols and / or stearates, wherein the wt.% relates to the total weight of the first aqueous component, and b) water glass selected from soda water glass, potassium water glass and / or lithium water glass, with a molar ratio of at least 2.6 as the second component, wherein the silicate two-component coating composition is free of polymers and VOCs, wherein the molar ratio indicates the ratio of silica, expressed as SiO2, to alkali oxide, expressed as Me2O = Na2O, K2O, Li2O, and is defined by the following formula: where MVG is the molar ratio, n(SiO2) is the molar amount of silica and n(Me2O) is the molar amount of alkali oxide.

2. A two-component silicate coating composition according to claim 1, wherein the water glass is potassium water glass.

3. A two-component silicate coating composition according to claim 1 or 2, wherein the water glass has a molar ratio in the range of 2.6 to 3.

4.

4. A silicate two-component coating composition according to any one of claims 1 to 3, wherein the mineral, alkali-stable pigment is selected from the group consisting of titanium dioxide, iron oxide red, iron oxide black, iron oxide yellow, cobalt blue, chromium oxide pigments, spinel phase pigments and combinations thereof.

5. A two-component silicate coating composition according to any one of claims 1 to 4, wherein the at least one filler is selected from quartz flour, precipitated or fumed silica, barium sulfate, magnesium carbonate, dolomite, calcium carbonate and combinations thereof.

6. A two-component silicate coating composition according to any one of claims 1 to 5, wherein the first aqueous component further contains one or more additives selected from thickeners, defoamers, dispersants, wetting agents and stabilizers.

7. A two-component silicate coating composition according to any one of claims 1 to 6, wherein the first aqueous component has a pH in the range of 10 to 13.

8. A two-component silicate coating composition according to any one of claims 1 to 7, which is free of polymers and VOCs, wherein the polymers are selected from the group consisting of polymer microplastics.

9. A method for applying a two-component coating composition to a substrate, comprising (a) providing a two-component coating composition according to any one of claims 1 to 7 and a substrate to be coated, (b) mixing the first component and the second component in a ratio ranging from 1:0.8 to 1:5 to obtain a mixed coating composition, and then within 1 hour (c) coating the substrate to be coated with the mixed coating composition, and (d) drying the coated substrate from step (c) for a period in the range of 0.5 to 24 hours at a temperature in the range of 30°C to 160°C.

10. The process according to claim 9, wherein the drying in step (d) takes place for a period in the range of 0.5 to 8 hours at a temperature in the range of 80°C to 150°C.

11. A method according to claim 9 or 10, which comprises a further wet coating step (c') after step (b) and before step (c), in which the mixed coating composition is first applied to the substrate immediately after its preparation and before its curing and then dried for a period in the range of 4 to 48 hours at a temperature in the range of 30°C to 160°C.

12. A method according to any one of claims 9 to 11, wherein no priming of the substrate takes place before it is coated in step (c).

13. The method according to any one of claims 9 to 12, wherein the substrate is a mineral substrate, preferably a fiber cement substrate or a concrete substrate.

14. The method of claim 13, wherein the substrate is selected from the group consisting of fiber cement boards, concrete roof tiles and paving stones.

15. A method according to any one of claims 9 to 14, wherein the substrate is stored under dry conditions for a period of at least one day prior to the coating step (c).

16. Coated substrate obtainable by the process according to any one of claims 9 to 15.

17. Use of the silicate two-component coating composition according to one of claims 1 to 8 for coating a mineral substrate, preferably a concrete substrate or a Fiber cement substrate, particularly preferred for industrial coating of concrete-containing substrates.

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